Multi-channel source assembly for downhole spectroscopy

Abstract

A multi-channel source assembly for downhole spectroscopy has individual sources that generate optical signals across a spectral range of wavelengths. A combining assembly optically combines the generated signals into a combined signal and a routing assembly that splits the combined signal into a reference channel and a measurement channel. Control circuitry electrically coupled to the sources modulates each of the sources at unique or independent frequencies during operation.

What is claimed is:  
     
       1. An assembly for downhole spectroscopy, comprising:
 a plurality of individual light emitting diode (LED) sources deployed downhole in the source assembly and generating optical signals across a spectral range of wavelengths; 
 a routing assembly deployed downhole in the source assembly, the routing assembly spectrally filtering the generated signals of the LED sources, concurrently combining the spectrally filtered signals through free space into a combined signal, and concurrently routing the combined signal through free space into a reference channel and one or more measurement channels; and 
 control circuitry deployed downhole in the source assembly, the control circuitry electrically coupled to the LED sources and operable to electronically modulate each of the LED sources at an independent frequency. 
 
     
     
       2. The assembly of  claim 1 , wherein the LED sources are selected from the group consisting of light emitting diodes (LEDs) and super-luminescent light emitting diodes (SLEDs). 
     
     
       3. The assembly of  claim 1 , wherein the LED sources provide:
 a continuous spectral distribution over a broad spectral range of wavelengths; or 
 a non-continuous spectral distribution of two or more spectrally continuous regions interposed by at least one spectrally dark region over a broad spectral range of wavelengths. 
 
     
     
       4. The assembly of  claim 1 , wherein the routing assembly comprises spectral filters selecting wavelengths and optical transmission characteristics of the optical signals from the LED sources. 
     
     
       5. The apparatus of  claim 4 , wherein the spectral filters are thermally stable for downhole conditions in which the source assembly deploys. 
     
     
       6. The assembly of  claim 1 , wherein the routing assembly comprises one or more optical elements spatially shaping the optical signals from the LED sources. 
     
     
       7. The assembly of  claim 1 , wherein the routing assembly comprises a splitter fractionally splitting the combined signal into the reference and the one or more measurement channels. 
     
     
       8. The apparatus of  claim 7 , wherein the splitter splits the combined signal into the reference channel disproportionately compared to the one or more measurement channels. 
     
     
       9. The assembly of  claim 1 , wherein the LED sources are spatially configured in an array topology arranged in one or more dimensions. 
     
     
       10. The assembly of  claim 9 , wherein the array typology is a two-dimensional array on a plane disposed parallel to a flow line; and wherein the routing assembly routes the spectrally filtered signals from the LED sources parallel to the plane and routes the reference and measurement channels orthogonal to the flow line. 
     
     
       11. The assembly of  claim 9 , wherein the routing assembly comprises:
 at least one first dichroic routing a first path of a first of the spectrally filtered signals from a first of the LED sources, the first LED source having a first wavelength; 
 at least one second dichroic combining the first path with a second path of a second of the spectrally filtered signals from a second of the LED sources, the second LED source having a second wavelength and disposed adjacent the first LED source in the array typology; and 
 at least one beam splitter splitting the combined paths of the spectrally filtered signals into the reference and measurement channels. 
 
     
     
       12. The assembly of  claim 11 , wherein the routing assembly comprises:
 at least one third dichroic routing a third path of a third of the spectrally filtered signals from a third of the LED sources, the third LED source having a third wavelength and disposed in a row of the array topology different than the first and second LED sources; 
 at least one beam combiner disposed between the at least one second dichroic and the at least one beam splitter and combining the third path of the third spectrally filtered signal with the combined first and second paths of the first and second spectrally filtered signals. 
 
     
     
       13. The assembly of  claim 9 , wherein the routing assembly comprises:
 a first filter disposed adjacent first and second of the LED sources, the first filter passing a first path of a first of the spectrally filtered signals from the first LED source and combining a second path of a second of the spectrally filtered signal reflected from the second LED source with the first path of the first spectrally filtered signal; and 
 a beam splitter splitting the combined paths of the spectrally filtered signals into the reference and measurement channels. 
 
     
     
       14. The assembly of  claim 13 , wherein the first filter comprises a low pass filter, and wherein the first LED source has a first wavelength less than a second wavelength of the second LED source. 
     
     
       15. The assembly of  claim 13 , wherein the first filter comprises a high pass filter, and wherein the first LED source has a first wavelength greater than a second wavelength of the second LED source. 
     
     
       16. The assembly of  claim 13 , wherein the routing assembly comprises:
 at least one second filter disposed before the beam splitter and disposed adjacent the first filter and at least one third of the LED sources, the at least one third filter passing the combined first and second paths of the first and second spectrally filtered signals and combining at least one third path of at least one third of the spectrally filtered signals reflected from the at least one third LED source with the combined first and second paths of the first and second spectrally filtered signals. 
 
     
     
       17. The assembly of  claim 1 , wherein to electronically modulate each of the LED sources, the control circuitry:
 turns each of the individual LED sources on and off; 
 electronically modulates each of the individual LED sources about a mean amplitude; 
 electronically modulates the individual LED sources at a unique frequency different from one another; or 
 electronically modulates the individual LED sources at the same frequency. 
 
     
     
       18. The assembly of  claim 1 , wherein the control circuitry receives input indicative of measured energy of the reference channel and controls an amplitude of the LED sources based on the input. 
     
     
       19. The assembly of  claim 1 , wherein the control circuitry electronically modulates the LED sources in:
 a first synchronous encoding mode in which the control circuitry operates each of two or more of the LED sources simultaneously using an independent frequency to generate optical signals, the first synchronous encoding mode enabling Fast-Fourier Transform analysis of the measurement and reference channels; 
 a second synchronous encoding mode in which the control circuitry operates the LED sources simultaneously using fixed frequency increments, the second synchronous encoding mode enabling deconvolution of the measurement and reference channels based on predefined temporal characteristics of the fixed frequency increments; 
 a first asynchronous encoding mode in which the control circuitry operates each of two or more of the LED sources in a serial fashion with only one of the LED sources in operation at any point in time, the first asynchronous encoding mode enabling raster scanning analysis of the measurement and reference channels; or 
 a second asynchronous encoding mode in which the control circuitry operates a unique sequence of subsets of the sources in a cyclic fashion with only one of the subsets of the LED sources in operation at a given point in time, the second asynchronous encoding mode enabling Hadamard Transform analysis of the measurement and reference channels. 
 
     
     
       20. The assembly of  claim 1 , further comprising:
 a tool housing deployable downhole and having a flow passage for a fluid sample; and 
 a fluid analysis device disposed in the tool housing relative to the flow passage, the fluid analysis device at least including the LED sources, the routing assembly, and the control circuitry. 
 
     
     
       21. A downhole fluid analysis method, comprising:
 deploying a fluid analysis device downhole; 
 obtaining a fluid sample downhole; 
 generating a plurality of optical signals across a spectrum of wavelengths by electronically modulating each of a plurality of light emitting diode (LED) sources at an independent frequency; 
 spectrally filtering the generated signals from one or more of the LED sources; 
 concurrently combining the spectrally filtered signals through free space into a combined signal; and 
 concurrently routing the combined signal through free space into one or more measurement channels for interacting with the fluid sample and into a reference channel for dynamically scaling the measurement channel. 
 
     
     
       22. The method of  claim 21 , wherein the LED sources are spatially configured in an array topology arranged in one or more dimensions. 
     
     
       23. The method of  claim 22 , wherein the array typology is a two-dimensional array on a plane disposed parallel to a flow line; and wherein routing the spectrally filtered signals comprises routing the spectrally filtered signals from the LED sources parallel to the plane and routing the reference and measurement channels orthogonal to the flow line. 
     
     
       24. The method of  claim 22 , wherein concurrently combining and routing comprises:
 routing, with a first dichroic, a first path of a first of the spectrally filtered signals from a first of the LED sources, the first LED source having a first wavelength; 
 combining, with a second dichroic, the first path with a second path of a second of the spectrally filtered signals from a second of the LED sources, the second LED source having a second wavelength and disposed adjacent the first LED source in the array typology; and 
 splitting, with at least one beam splitter, the combined paths of the spectrally filtered signals into the reference and measurement channels. 
 
     
     
       25. The method of  claim 24 , wherein concurrently combining and routing comprises:
 routing, with at least one third dichroic, a third path of a third of the spectrally filtered signals from a third of the LED sources, the third LED source having a third wavelength and disposed in a row of the array topology different than the first and second LED sources; and 
 combining, with at least one beam combiner disposed between the second dichroic and the beam splitter, the third path of the third spectrally filtered signal with the combined first and second paths of the first and second spectrally filtered signals. 
 
     
     
       26. The method of  claim 22 , wherein concurrently combining and routing comprises:
 passing, with a first filter disposed adjacent first and second of the LED sources, a first path of a first of the spectrally filtered signals from the first LED source; 
 combining, with the first filter, a second path of a second of the spectrally filtered signal reflected from the second LED source with the first path of the first spectrally filtered signal; and 
 splitting, with a beam splitter, the combined paths of the spectrally filtered signals into the reference and measurement channels. 
 
     
     
       27. The method of  claim 26 , wherein the first filter comprises a low pass filter, and wherein the first LED source has a first wavelength less than a second wavelength of the second LED source. 
     
     
       28. The method of  claim 26 , wherein the first filter comprises a high pass filter, and wherein the first LED source has a first wavelength greater than a second wavelength of the second LED source. 
     
     
       29. The method of  claim 26 , wherein concurrently combining and routing comprises:
 passing the combined first and second paths of the first and second spectrally filtered signals with at least one second filter disposed before the beam splitter and disposed adjacent the first filter and at least one third of the LED sources; and 
 combining, with the at least one third filter, at least one third path of at least one third of the spectrally filtered signals reflected from the at least one third LED source with the combined first and second paths of the first and second spectrally filtered signals. 
 
     
     
       30. The method of  claim 21 , wherein modulating each of the LED sources comprises:
 turning each of the individual LED sources on and off; 
 modulating each of the individual LED sources about a mean amplitude; 
 modulating one or more of the individual LED sources at the same frequency; or 
 modulating one or more of the individual LED sources at unique frequencies different from one another. 
 
     
     
       31. The method of  claim 21 , wherein spectrally filtering the generated signals from the one or more LED sources comprises selecting wavelengths and optical transmission characteristics of the generated signals from the one or more LED sources. 
     
     
       32. The method of  claim 21 , wherein routing the combined signal comprises fractionally splitting the combined signal into the reference and measurement channels. 
     
     
       33. The apparatus of  claim 32 , wherein fractionally splitting the combined signal into the reference and measurement channels comprises splitting the combined signal into the reference channel disproportionally compared to the measurement channel. 
     
     
       34. The method of  claim 21 , wherein modulating each of a plurality of LED sources is controlled based on measured energy of the reference channel. 
     
     
       35. The method of  claim 21 , wherein modulating each of a plurality of LED sources comprises:
 synchronously encoding the LED sources by simultaneously operating each of two or more of the LED sources and modulating each with an independent frequency; 
 synchronously encoding the LED sources by operating the LED sources simultaneously using fixed frequency increments; 
 asynchronously encoding the LED sources by operating each of two or more of the LED sources in a serial fashion with only one of the LED sources in operation at any point in time; or 
 asynchronously encoding the sources by operating a unique sequence of subsets of the LED sources in a cyclic fashion with only one of the subsets of the LED sources in operation at a given point in time.